The present invention relates to a compact steam turbine and particularly to a high temperature steam turbine in which a 12% Cr based steel is used for final stage rotating blade of a low pressure steam turbine.
The rotating blade for a steam turbine is made from a 12Crxe2x80x94Moxe2x80x94Nixe2x80x94Vxe2x80x94N steel at the present time. In recent years, there is a desire to improve the thermal efficiency of the gas turbine from the viewpoint of energy saving and to make the equipment of the gas turbine more compact from the viewpoint of space savings.
To improve the thermal efficiency of a gas turbine and to make the equipment thereof more compact, it is effective to make the blades of the steam turbine longer, and for this purpose, there has been a tendency to make the length of the final stage blades of the low pressure steam turbine longer every year. With such a tendency the service condition for the blades of a steam turbine becomes strict, and as a result, the 12Crxe2x80x94Moxe2x80x94Nixe2x80x94Vxe2x80x94N steel is no longer sufficient in strength under the above service conditions, and therefore, it is expected that a new material will be developed having a higher strength. The strength of the material for the blades of the steam turbine is determined by its tensile strength which is a basic mechanical characteristic.
The material for the blades of a steam turbine is also required to exhibit a high toughness in addition to a high strength for ensuring safety against breakage.
As a structural material having a tensile strength higher than that of the conventional 12 Crxe2x80x94Moxe2x80x94Nixe2x80x94Vxe2x80x94N steel (martensite based steel), there are generally known a Ni based alloy and a Co based alloy; however, such materials are undesirable as blade materials because of their poor working ability at hot temperatures, poor machinability, and periodic damping characteristic.
A disk material for a gas turbine is known, for example, from Japanese Patent Laid-open Nos. Sho 63-171856 and Hei 4-120246.
In the conventional steam turbine, the maximum steam temperature has been set at 566xc2x0 C. and the maximum steam pressure has been set at 246 atg.
However, from the viewpoint of exhaustion of fossil fuel such as mineral oil or coal, energy saving, and prevention of environmental pollution, it is desired to increase the efficiency of the thermal power-generation plant, and to increase the efficiency of power-generation, it is most effective to increase the steam temperature of the steam turbine. A suitable material for such a high efficient ultra-high temperature steam turbine is known from Japanese Patent Laid-open No. Hei 7-233704.
The present invention has been made to cope with the recent trend to make the blades of a low pressure steam turbine longer. A suitable material for the rotating blades for a steam turbine is not disclosed in Japanese Patent Laid-open Nos. Sho 63-171856 and Hei 4-120246 at all.
Japanese Patent Laid-open No. Hei 7-233704 discloses a rotor material, a casing material, and the like; however, as described above, the document does not describe a 12% Cr based martensite steel for a final stage rotating blade for a high pressure side turbine-intermediate pressure side turbine integral type steam turbine and a low pressure steam turbine which are operated at high temperatures.
An object of the present invention is to provide a steam turbine operable at a high temperature in a range of 600 to 660xc2x0 C. by use of ferrite based heat resisting steels, to thereby enhance the thermal efficiency, and a steam turbine power-generation plant using the steam turbine.
Another object of the present invention is to provide a steam turbine operable at each operating temperature in a range of 600 to 660xc2x0 C. with its basic structure being substantially not changed, and a steam turbine power-generation plant using the steam turbine.
The present invention provides a steam turbine power-generation plant including a combination of a high pressure turbine, an intermediate pressure turbine and two low pressure turbines, a combination of a high pressure turbine and a low pressure turbine connected to each other and an intermediate pressure turbine and a low pressure turbine connected to each other, or a combination of a high pressure side turbine-intermediate pressure side turbine integral steam turbine and one low pressure turbine or two low pressure turbines connected in tandem with each other, in which the temperature of a steam inlet to a first stage rotating blade of each of the high pressure turbine and the intermediate pressure turbine or the high pressure/intermediate pressure turbine is in a range of 600 to 660xc2x0 C. (preferably, 600 to 620xc2x0 C., 620 to 630xc2x0 C., 630 to 640xc2x0 C.) and the temperature of a steam inlet to a first stage rotating blade of the low pressure turbine is in a range of 350 to 400xc2x0 C., characterized in that a rotor shaft, rotating blades, stationary blades, and an inner casing, exposed to the temperature atmosphere of the steam inlet, of each of the high pressure turbine and the intermediate pressure turbine or the high pressure/intermediate pressure turbine are made from a high strength martensite steel containing Cr in an amount of 8 to 13 wt %; and a final stage rotating blade of the low pressure turbine is specified such that a value of [the length of a blade (inch)xc3x97the number of revolution (rpm)] is 125,000 or more.
The present invention provides a steam turbine, particularly, a high pressure side turbine-intermediate pressure side turbine integral type steam turbine in which steam discharged from a high pressure side turbine is heated at a temperature equal to or higher than an inlet temperature on the high pressure side and fed in an intermediate pressure turbine, the steam turbine including a rotor shaft, rotating blades planted in the rotor shaft, stationary blades for guiding flow of steam to the rotating blades, and an inner casing for holding the stationary blades, in which the temperature of the steam flowing to a first stage one of the rotating blades is in a range of 600 to 660xc2x0 C. and the pressure is 250 kgf/cm2 or more (preferably 246 to 316 kgf/cm2) or 170 to 200 kgf/cm2, characterized in that the rotor shaft or the rotor shaft, at least a first stage one of the rotating blades, and a first stage one of the stationary blades are made from a high strength martensite steel containing Cr in an amount of 9.5 to 13 wt % (preferably, 10.5 to 11.5 wt %) and having a full temper martensite structure, the martensite steel being specified such that a 105 h creep rupture strength thereof at a temperature corresponding to each steam temperature (preferably, 610xc2x0 C., 625xc2x0 C., 640xc2x0 C., 650xc2x0 C., 660xc2x0 C.) is in a range of 10 kgf/mm2 or more (preferably, 17 kgf/mm2 or more); and the inner casing is made from a martensite cast steel containing Cr in an amount of 8 to 9.5 wt %, the martensite steel being specified such that the 105 h creep rupture strength at the temperature corresponding to the steam temperature is in a range of 10 kgf/mm2 or more (preferably, 10.5 kgf/mm2 or more).
In the high pressure turbine and the intermediate pressure turbine or the high pressure side turbine-intermediate pressure side turbine integral type steam turbine, preferably, the rotor shaft, at least a first stage one of the rotating blades, and a first stage one of the stationary blades, which are preferably used at a steam temperature of 620 to 640xc2x0 C., are made from a high strength martensite steel containing 0.05 to 0.20 wt % of C, 0.15 wt % or less of Si, 0.05 to 1.5 wt % of Mn, 9.5 to 13 wt % of Cr, 0.05 to 1.0 wt % of Ni, 0.05 to 0.35 wt % of V, 0.01 to 0.20 wt % of Nb, 0.01 to 0.06 wt % of N, 0.05 to 0.5 wt % of Mo, 1.0 to 4.0 wt % of W, 2 to 10 wt % of Co, and 0.0005 to 0.03 wt % of B, the balance being 78 wt % or more of Fe; and the rotor shaft, at least a first stage one of the rotating blades, and a first stage one of the stationary blades, which are preferably used at a steam temperature of 600 to less than 620xc2x0 C., are made from a high strength martensite steel containing 0.1 to 0.25 wt % of C, 0.6 wt % or less of Si, 1.5 wt % or less of Mn, 8.5 to 13 wt % of Cr, 0.05 to 1.0 wt % of Ni, 0.05 to 0.5 wt % of V, 0.10 to 0.65 wt % of W and 0.1 wt % or less of Al, the balance being 80 wt % or more of Fe. Further, the above inner casing is preferably made from a high strength martensite steel containing 0.06 to 0.16 wt % of C, 0.5 wt % or less of Si, 1 wt % or less of Mn, 0.2 to 1.0 wt % of Ni, 8 to 12 wt % of Cr, 0.05 to 0.35 wt % of V, 0.01 to 0.15 wt % of Nb, 0.01 to 0.8 wt % of N, 1 wt % or less of Mo, 1 to 4 wt % of W, and 0.0005 to 0.003 wt % of B, the balance being 85 wt % or more of Fe.
In the high pressure steam turbine according to the present invention, preferably, nine stages or more, preferably, ten stages or more of the rotating blades are provided and the first stage one of the rotating blades is of a double-flow type; and the rotor shaft is made from a high strength martensite steel containing Cr in an amount of 9 to 13 wt %, the rotor shaft being specified such that a distance (L) between centers of bearings provided for the rotor shaft is 5000 mm or more (preferably, 5100 to 6500 mm), the minimum diameter (D) of portions, of the rotor shaft, corresponding to the stationary blades is 660 mm or more (preferably, 680 to 740 mm), and the ratio (L/D) is in a range of 6.8 to 9.9 (preferably, 7.9 to 8.7).
In the intermediate pressure steam turbine according to the present invention, preferably, the rotating blades have a double-flow structure in which two sets, each being composed of six stages or more of the rotating blades, are symmetrically disposed right and left and a first stage one of the rotating blade is planted at the central portion of the rotor shaft; and the rotor shaft is made from a high strength martensite steel containing Cr in an amount of 9 to 13 wt %, the rotor shaft being specified such that a distance (L) between centers of bearings provided for the rotor shaft is 5000 mm or more (preferably, 5100 to 6500 mm), the minimum diameter (D) of portions, of the rotor shaft, corresponding to the stationary blades is 630 mm or more (preferably, 650 to 710 mm), and the ratio (L/D) is in a range of 7.0 to 9.2 (preferably, 7.8 to 8.3).
The present invention provides a low pressure steam turbine separately having a high pressure turbine and an intermediate pressure turbine, characterized in that the rotating blades has a double-flow structure in which two sets, each being composed of six stages or more of the rotating blades, are symmetrically disposed right and left, and a first stage one of the rotating blades is planted at a central portion of the rotor shaft; the rotor shaft is made from a Nixe2x80x94Crxe2x80x94Moxe2x80x94V based low alloy steel containing Ni in an amount of 3.25 to 4.25 wt %, the rotor shaft being specified such that a distance (L) between centers of bearings provided for the rotor shaft is 6500 mm or more (preferably, 6600 to 7100 mm), the minimum diameter (D) of portions, of the rotor shaft, corresponding to the stationary blades is 750 mm or more (preferably, 760 to 900 mm), and the ratio (L/D) is in a range of 7.8 to 10.2 (preferably, 8.0 to 8.6); and a final stage one of the rotating blades is made from a high strength martensite steel, the final stage rotating blade being specified such that a value of [the length of a blade (inch)xc3x97the number of revolution (rpm)] is 125,000 or more.
The present invention provides a steam turbine power-generation plant including a combination of a high pressure turbine, an intermediate pressure turbine and two low pressure turbines, a combination of a high pressure turbine and a low pressure turbine connected to each other and an intermediate pressure turbine and a low pressure turbine connected to each other, or a combination of a high pressure side turbine-intermediate pressure side turbine integral steam turbine and one low pressure turbine or two low pressure turbines connected in tandem with each other, in which the temperature of a steam inlet to a first stage rotating blade of each of the high pressure turbine and the intermediate pressure turbine or the high pressure/intermediate pressure turbine is in a range of 600 to 660xc2x0 C. and the temperature of a steam inlet to a first stage rotating blade of the low pressure turbine is in a range of 350 to 400xc2x0 C.; the metal temperature of each of the first stage rotating blade planted portion and the first stage rotating blade of the rotor shaft of the high pressure turbine is not allowed to be lower, 40xc2x0 C. or more, than the temperature of the steam inlet to the first stage rotating blade of the high pressure turbine (preferably, lower 20-35xc2x0 C. than the steam temperature); and the metal temperature of each of the first stage rotating blade planted portion and the first stage rotating blade of the rotor shaft of the intermediate pressure turbine is not allowed to be lower, 75xc2x0 C. or more, than the temperature of the steam inlet to the first stage rotating blade of the intermediate pressure turbine (preferably, lower 50-70xc2x0 C. than the steam temperature), characterized in that the rotor shaft and at least the first stage rotating blade of each of the high pressure turbine and the intermediate pressure turbine are made from a martensite steel containing Cr in an amount of 9.5 to 13 wt %; and a final stage one of the rotating blades is made from a high strength martensite steel, the final stage rotating blade being specified such that a value of [the length of a blade (inch)xc3x97the number of revolution (rpm)] is 125,000 or more.
The present invention provides a coal burning thermal power-generation plant including a coal burning boiler, a steam turbine driven by steam produced by the boiler, a single or double generators driven by the steam turbine to generate a power of 1000 MW or more, characterized in that the steam turbine has a combination of a high pressure turbine, an intermediate pressure turbine and two low pressure turbines, a combination of a high pressure turbine and a low pressure turbine connected to each other and an intermediate pressure turbine and a low pressure turbine connected to each other, or a combination of a high pressure side turbine-intermediate pressure side turbine integral steam turbine and one low pressure turbine or two low pressure turbines connected in tandem with each other; the temperature of a steam inlet to a first stage rotating blade of each of the high pressure turbine and the intermediate pressure turbine or the high pressure/intermediate pressure turbine is in a range of 600 to 660xc2x0 C. and the temperature of a steam inlet to a first stage rotating blade of the low pressure turbine is in a range of 350 to 400xc2x0 C.; steam heated at a temperature higher 3xc2x0 C. or more (preferably, 3 to 10xc2x0 C., more preferably, 3 to 7xc2x0 C.) than the temperature of the steam inlet to the first stage rotating blade of the high pressure turbine by a superheater of the boiler is allowed to flow to the first stage rotating blade of the high pressure turbine; the steam discharged from the high pressure turbine is heated at a temperature higher 2xc2x0 C. or more (preferably, 2 to 10xc2x0 C., more preferably, 2 to 5xc2x0 C.) than the temperature of the steam inlet of the first stage rotating blade of the intermediate pressure blade by a re-heater of the boiler and is allowed to flow to the first stage rotating blade of the intermediate pressure turbine; and the steam discharged from the intermediate pressure turbine is heated at a temperature higher 3xc2x0 C. or more (preferably, 3 to 10xc2x0 C., more preferably, 3 to 6xc2x0 C.) than the temperature of the steam inlet to the first stage rotating blade of the low pressure turbine by an economizer of the boiler and is allowed to flow to the first stage rotating blade of the low pressure turbine; and a final stage one of the rotating blades of the low pressure turbine is made from a high strength martensite steel, the final stage rotating blade being specified such that a value of [the length of a blade (inch)xc3x97the number of revolution (rpm)] is 125,000 or more.
In the above low pressure steam turbine having the high pressure turbine and the intermediate pressure turbine or the high pressure/intermediate pressure integral turbine, preferably, the temperature of a steam inlet to a first stage one of the rotating blades is in a range of 350 to 400xc2x0 C. (preferably, 360 to 380xc2x0 C.); and the rotor shaft is made from a low alloy steel containing 0.2 to 0.3 wt % of C, 0.05 wt % or less of Si, 0.1 wt % or less of Mn, 3.25 to 4.25 wt % of Ni, 1.25 to 2.25 wt % of Cr, 0.07 to 0.20 wt % of Mo, and 0.07 to 0.2 wt % of V, the balance being 92.5 wt % or more of Fe.
In the above high pressure steam turbine, preferably, seven stages or more (preferably, nine to twelve stages) of the rotating blades are provided; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 25 to 180 mm; the diameter of a rotating blade planted portion of the rotor shaft is larger than the diameter of a portion, of the rotor shaft, corresponding to the stationary shaft; the axial root width of the rotating blade planted portion becomes stepwise larger from the upstream side to the downstream side in three steps or more (preferably, in four to seven steps); the ratio of the axial root width of the rotating blade planted portion to the length of the blade portion is in a range of 0.2 to 1.6 (preferably, 0.30 to 1.30, more preferably, 0.65 to 0.95) and becomes smaller from the upstream side to the downstream side.
In the above high pressure steam turbine, preferably, seven stages or more (preferably, nine stages or more) of the rotating blades are provided; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 25 to 180 mm; and the ratio between the lengths of the blade portions of the adjacent ones of the rotating blades is in a range of 2.3 or less and becomes gradually larger to the downstream side, and the length of the blade portion becomes larger from the upstream side to the downstream side.
In the above high pressure steam turbine, preferably, seven stages or more (preferably, nine stages or more) of the rotating blades are provided; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 25 to 180 mm; and the axial width of a portion, of the rotor shaft, corresponding to the stationary blade becomes stepwise smaller from the upstream side to the downstream side in two steps or more (preferably, in two to four steps), and the ratio of the above axial width to the length of the blade portion of the rotating blade on the downstream side is in a range of 4.5 or less and becomes stepwise smaller to the downstream side.
In the above intermediate pressure steam turbine, preferably, the rotating blades have a double-flow structure in which two steps, each being composed of six stages or more (preferably, six to nine stages) of the rotating blades, are symmetrically disposed right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 60 to 300 mm; the diameter of a rotating blade planted portion of the rotor shaft is larger than the diameter of a portion, of the rotor shaft, corresponding to the stationary shaft; the axial root width of the rotating blade planted portion becomes stepwise larger from the upstream side to the downstream side in two steps or more (preferably, in two to six steps); the ratio of the axial root width of the rotating blade planted portion to the length of the blade portion is in a range of 0.35 to 0.80 (preferably, 0.5 to 0.7) and becomes smaller from the upstream side to the downstream side.
In the above intermediate pressure steam turbine, preferably, the rotating blades have a double-flow structure in which two steps, each being composed of six stages or more of the rotating blades, are symmetrically disposed right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 60 to 300 mm; and the length of the blade portion becomes larger from the upstream side to the downstream side, and the ratio between the lengths of the blade portions of the adjacent ones of the rotating blades is in a range of 1.3 or less (preferably, 1.1 to 1.2) and becomes gradually larger to the downstream side.
In the above intermediate pressure steam turbine, preferably, the rotating blades have a double-flow structure in which two steps, each being composed of six stages or more of the rotating blades, are symmetrically disposed right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 60 to 300 mm; and the axial width of the portion, of the rotor shaft, corresponding to the stationary blade becomes stepwise smaller from the upstream side to the downstream side in two steps or more (preferably, in three to six steps), and the ratio of the above axial width to the length of the blade portion of the rotating blade on the downstream side is in a range of 0.80 to 2.50 (preferably, 1.0 to 2.0) and becomes stepwise smaller to the downstream side.
In the above low pressure steam turbine in the power-generation plant in which the high pressure turbine and the intermediate pressure turbine are separately provided, preferably, the rotating blades have a double-flow structure in which two steps, each being composed of six stages or more (preferably, eight to ten stages) of the rotating blades, are symmetrically disposed right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 80 to 1300 mm; the diameter of a rotating blade planted portion of the rotor shaft is larger than the diameter of a portion, of the rotor shaft, corresponding to the stationary shaft; the axial root width of the rotating blade planted portion becomes stepwise larger from the upstream side to the downstream side in three steps or more (preferably, in four to seven steps); and the ratio of the axial root width of the rotating blade planted portion to the length of the blade portion is in a range of 0.2 to 0.7 (preferably, 0.3 to 0.55) and becomes smaller from the upstream side to the downstream side.
In the above low pressure steam turbine in the power-generation plant in which the high pressure turbine and the intermediate pressure turbine are separately provided, preferably, the rotating blades have a double-flow structure in which two sets, each being composed of six stages or more of the rotating blades, are symmetrically disposed right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 80 to 1300 mm; and the length of the blade portion becomes larger from the upstream side to the downstream side, and the ratio between the lengths of the blade portions of the adjacent ones of the rotating blades is in a range of 1.2 to 1.8 (preferably, 1.4 to 1.6) and becomes gradually larger to the downstream side.
In the above low pressure steam turbine, preferably, the rotating blades have a double-flow structure in which two sets, each being composed of six stages or more, preferably, eight stages or more of the rotating blades, are symmetrically disposed right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 80 to 1300 mm; the axial width of the portion, of the rotor shaft, corresponding to the stationary blade becomes stepwise larger from the upstream side to the downstream side, preferably, in three stages or more (more preferably, four to seven stages); and the ratio between the lengths of the blade portions of the adjacent ones of the rotating blades is in a range of 0.2 to 1.4 (preferably, 0.25 to 1.25, more preferably, 0.5 to 0.9) and becomes stepwise smaller to the downstream side.
In the above high pressure steam turbine, seven stages or more, preferably, nine stages or more of the rotating blades are provided; the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is smaller than the rotating blade planted portion of the rotor shaft; the axial width of the portion corresponding to the stationary blade becomes stepwise larger from the downstream side to the upstream side of the steam flow in two steps or more (preferably, two or four steps); the width of the portion corresponding to the stationary blade between the final stage rotating blade and the preceding stage rotating blade is 0.75 to 0.95 times (preferably, 0.8 to 0.9 times, more preferably, 0.82 to 0.88 times) the width between the second stage rotating blade and the third stage rotating blade; the axial width of the rotating blade planted portion of the rotor shaft becomes stepwise larger from the upstream side to the downstream side of the steam flow in three steps or more (preferably, four to seven steps); and the axial width of the final stage rotating blade is 1 to 2 times (preferably, 1.4 to 1.7 times) the axial width of the second stage rotating blade.
In the above intermediate pressure steam turbine, preferably, six stages or more the rotating blades are provided; the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is smaller than the diameter of the rotating blade planted portion of the rotor shaft; the axial width of the portion corresponding to the stationary blade becomes stepwise larger from the downstream side to the upstream side of the steam flow in two steps or more (preferably, three or six steps); the width of the portion corresponding to the stationary blade between the final stage rotating blade and the preceding stage rotating blade is 0.5 to 0.9 times (preferably, 0.65 to 0.75 times) the width between the first stage rotating blade and the second stage rotating blade; the axial width of the rotating blade planted portion of the rotor shaft becomes stepwise larger from the upstream side to the downstream side of the steam flow in two steps or more (preferably, three to six steps); and the axial width of the final stage rotating blade is 0.8 to 2 times (preferably, 1.2 to 1.5 times) the axial width of the final stage rotating blade.
In the above low pressure steam turbine, the rotating blades have a double-flow structure in which two sets, each being composed of eight stages or more of the rotating blades, are symmetrically disposed right and left; the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is smaller than the rotating blade planted portion of the rotor shaft; the axial width of the portion corresponding to the stationary blade becomes stepwise larger from the downstream side to the upstream side of the steam flow, preferably, in three steps or more (more preferably, four or seventh steps); the width of the portion corresponding to the stationary blade between the final stage rotating blade and the preceding stage rotating blade is 1.5 to 3.0 times (preferably, 2.0 to 2.7 times) the width between the first stage rotating blade and the second stage rotating blade; the axial width of the rotating blade planted portion of the rotor shaft becomes stepwise larger from the upstream side to the downstream side of the stem flow, preferably, in three steps or more (preferably, four to seven steps); and the axial width of the final stage rotating blade is 5 to 8 times (preferably, 6.2 to 7.0 times) the axial width of the final stage rotating blade.
Each of the above high pressure turbine, intermediate pressure turbine, high pressure/intermediate pressure integral turbine, and low pressure turbine can be used at each of service steam temperatures in a range of 610 to 660xc2x0 C. with the same structure.
It is desired to adjust the composition of the rotor material of the present invention, having a full temper martensite structure, such that the Cr equivalent calculated by the following equation is set in a range of 4 to 8 wt % for obtaining a high temperature strength, a high low temperature toughness, and a high fatigue strength.
The high pressure side turbine-intermediate pressure side turbine integral type steam turbine of the present invention is characterized in that seven stages or more, preferably, eight stages or more of the rotating blades are provided on the high pressure side and five stages or more, preferably, six stages or more of the rotating blades are provided on the intermediate pressure side; and the rotor shaft is made from a high strength martensite steel containing Cr in an amount of 9 to 13 wt %, the rotor shaft being specified such that a distance (L) between centers of bearings provided for the rotor shaft is 6000 mm or more (preferably, 6100 to 7000 mm), the minimum diameter (D) of portions, of the rotor shaft, corresponding to the stationary blades is 660 mm or more (preferably, 620 to 760 mm), and the ratio (L/D) is in a range of 8.0 to 11.3 (preferably, 9.0 to 10.0).
The low pressure steam turbine used in combination with the high pressure/intermediate pressure integral type turbine has the following feature. In the low pressure steam turbine, the rotating blades have a double-flow structure in which two sets, each being composed of five stages or more, preferably, six stages or more of the rotating blades, are symmetrically disposed right and left, and a first stage one of the rotating blades is planted at a central portion of the rotor shaft; the rotor shaft is made from a Nixe2x80x94Crxe2x80x94Moxe2x80x94V based low alloy steel containing Ni in an amount of 3.25 to 4.25 wt %, the rotor shaft being specified such that a distance (L) between centers of bearings provided for the rotor shaft is 6500 mm or more (preferably, 6600 to 7500 mm), the minimum diameter (D) of portions, of the rotor shaft, corresponding to the stationary blades is 750 mm or more (preferably, 760 to 900 mm), and the ratio (L/D) is in a range of 7.8 to 10.0 (preferably, 8.0 to 9.0); and a final stage one of the rotating blades is made from a high strength martensite steel, the final stage rotating blade being specified such that a value of [the length of a blade (inch)xc3x97the number of revolution (rpm)] is 125,000 or more.
The above rotor shaft is made from a low alloy steel containing 0.2 to 0.3 wt % of C, 0.05 wt % or less of Si, 0.1 wt % or less of Mn, 3.0 to 4.5 wt % of Ni, 1.25 to 2.25 wt % of Cr, 0.007 to 0.20 wt % of Mo, and 0.07 to 0.2 wt % of V, the balance being 92.5 wt % or more of Fe, the rotor shaft being specified such that the diameter (D) of the portion, of the rotor shaft, corresponding to the stationary blade is in a range of 750 to 1300 mm and the diameter (L) between centers of bearings provided for the rotor shaft is 5.0 to 9.5 times the diameter (D).
The above rotating blades have double-flow structure in which two sets, each being composed of five stages or more, preferably, six stages or more of the rotating blades are symmetrically provided right and left; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream of the steam flow is in a range of 80 to 1300 mm; the diameter of the rotating blade planted portion of the rotor shaft is larger the diameter of the portion, of the rotor shaft, corresponding to the stationary blade; the axial root width of the rotating blade planted portion of the rotor shaft is extended downward to be larger than the blade planted portion and becomes stepwise smaller from the downstream side to the upstream side; and the ratio of the axial root width of the rotating blade planted portion to the length of the blade portion is in a range of 0.25 to 0.80.
The above rotating blades has a double-flow structure in which two sets, each being composed of five stages or more, preferably, six stages or more of the rotating blades are symmetrically provided right and left; the length of a blade portion of each of the rotating blades is in a range of 80 to 1300 mm and becomes gradually larger from the upstream side to the downstream side; and the ratio between the lengths of the blade portions of the adjacent ones of the rotating blades is in a range of 1.2 to 1.7.
The above rotating blades has a double-flow structure in which two sets, each being composed of five stages or more, preferably, six stages or more of the rotating blades are symmetrically provided right and left; the length of a blade portion of each of the rotating blades is in a range of 80 to 1300 mm and becomes larger from the upstream side to the downstream side; the axial root width of the rotating blade planted portion of the rotor shaft becomes larger from the upstream side to the downstream side at least in three steps, and is extend downward to be larger than the width of the rotating blade planted portion.
The high pressure side turbine-intermediate pressure side turbine integral type steam turbine according to the present invention has the following configuration:
Seven stages or more of the rotating blades are provided on the high pressure side; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 40 to 200 mm; the diameter of a rotating blade planted portion of the rotor shaft is larger than the diameter of a portion, of the rotor shaft, corresponding to the stationary shaft; the axial root width of the rotating blade planted portion becomes stepwise larger from the upstream side to the downstream side; the ratio of the axial root width of the rotating blade planted portion to the length of the blade portion is in a range of 0.20 to 1.60, preferably, 0.25 to 1.30 and becomes larger from the upstream side to the downstream side; and two sets, each being composed of five stages or more of the rotating blades, are symmetrically provided right and left on the intermediate pressure side; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 100 to 350 mm; the diameter of a rotating blade planted portion of the rotor shaft is larger than the diameter of a portion, of the rotor shaft, corresponding to the stationary shaft; the axial root width of the rotating blade planted portion becomes smaller from the upstream side to the downstream side except for the final stage; the ratio of the axial root width of the rotating blade planted portion to the length of the blade portion is in a range of 0.35 to 0.80, preferably, 0.40 to 0.75 and becomes smaller from the upstream side to the downstream side.
Further, seven stages or more of the rotating blades are provided on the high pressure side; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side of the steam flow is in a range of 25 to 200 mm; and the ratio between the lengths of the blade portions of the adjacent ones of the rotating blades is in a range of 1.05 to 1.35 and the length of the blade portion of 100 to 350 mm; and the ratio between the blade portions becomes gradually larger from the upstream side to the downstream side; and five stages or more of the rotating blades are provided on the intermediate pressure portion; the length of a blade portion of each of the rotating blades arranged from the upstream side to the downstream side is in a range of the adjacent ones of the rotating blades is in a range of 1.10 to 1.30 and the length of the blade portion of the rotating blade becomes gradually larger from the upstream side to the downstream side.
Further, six stages or more, preferably, seven stages or more of the rotating blades are provided on the high pressure side; the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is smaller than the diameter of the rotating blade planted portion of the rotor shaft; the axial root width of the rotating blade portion is widest at the first stage and becomes stepwise larger from the upstream side to the downstream side in two steps or more, preferably, in three steps or more; five stages or more of the rotating blades are provided on the intermediate pressure side; the diameter of the portion, of the rotor shaft, corresponding to the stationary blade is smaller than the diameter of the rotating blade planted portion of the rotor shaft; the axial root width of the rotating blade portion is stepwise changed on the upstream side as compared with the downstream side, preferably, in four steps or more; and the axial root width at the first stage is larger than that at the second stage, the axial root width at the final stage is larger than that at each of the other stages, and the axial root width at each of the first stage and the second stage is extended downward.
The present invention provides a steam turbine long blade characterized in that the steam turbine is made from a martensite steel containing 0.08 to 0.18 wt % of C, 0.25 wt % or less of Si, 0.90 wt % or less of Mn, 8.0 to 13.0 wt % of Cr, 2 to 3 wt % or less of Ni, 1.5 to 3.0 wt % of Mo, 0.05 to 0.35 wt % of V, 0.02 to 0.20 wt % in total of one kind or two kinds of Nb and Ta, and 0.02 to 0.10 wt % of N.
The above steam turbine long blade, which is required to withstand a high centrifugal force and a vibrational stress caused by high speed rotation, must be high in both the tensile strength and high cyclic fatigue strength. Consequently, the blade material is required to have a full temper martensite structure for eliminating the undesirable xcex4 ferrite which significantly reduces the fatigue strength.
The inventive steel is characterized in that it does not contain a xcex4 ferrite phase substantially by adjusting the composition such that the Cr equivalent calculated by the above equation is 10 or less.
The tensile strength of the long blade material steel is 120 kgf/mm2 or more, preferably, 128.5 kgf/mm2 or more.
To obtain a steam turbine long blade material which is homogeneous and high in strength, a forged product obtained from an ingot is subjected to the following heat-treatments [(quenching and temper (twice)]; namely, the product is kept at a temperature of 1000 to 1100xc2x0 C., preferably, for 0.5 to 3 h and is rapidly cooled to room temperature (quenching), and heated to a temperature of 550 to 570xc2x0 C. and kept at the temperature, preferably, for 1 to 6 h and cooled to room temperature (primary temper) and then heated to a temperature of 560 to 590xc2x0 C. and kept at the temperature, preferably, for 1 to 6 h and cooled to room temperature (secondary temper).
According to the present invention, in the steam turbine (number of revolution: 3600 rpm), the length of the final stage blade portion of the low pressure turbine is set at 914 mm (36xe2x80x3) or more, preferably, 965 mm (38xe2x80x3) or more; and in the steam turbine (number of revolution: 3000 rpm), the length of the final stage blade portion of the low pressure turbine is set at 1092 mm (43xe2x80x3) or more, preferably, 1168 mm (46xe2x80x3) or more. Further, [the length of a blade portion (inch)]xc3x97the number of revolution (rpm)] is set at 125,000 or more, preferably, 138,000 or more.
In the heat resisting cast steel as the casing material according to the present invention, to enhance the high temperature strength, low temperature toughness and fatigue strength by adjusting the alloy composition such that the alloy has a temper martensite of 95% or more (xcex4 ferrite: 5% or less), the alloy composition is preferably adjusted such that the Cr equivalent calculated by the following equation (the content of each element is expressed in wt %) is in a range of 4 to 10.
Cr equivalent=Cr+6Si+4Mo+1.5W+11V+5Nbxe2x88x9240Cxe2x88x9230Nxe2x88x9230Bxe2x88x922Mnxe2x88x924Nixe2x88x922Co+2.5 Ta
In the 12Cr based heat resisting steel of the present invention, particularly, when used in steam at a temperature of 625xc2x0 C. or more, the material preferably exhibits a 105 h creep rupture strength of 10 kgf/mm2 or more and an impact absorption energy (at room temperature) of 1 kgf-m or more.
(1) There will be described the reason for limiting the content of each component of the 12% Cr based steel used for the final stage blade of the low pressure steam turbine according to the present invention.
C is required to be added in an amount of 0.08 wt % at minimum for ensuring the tensile strength. When C is added in an excessively large amount, the toughness is reduced. The content of C must be 0.20 wt % or less. In particular, the content of C is, preferably, 0.10 to 0.18 wt %, more preferably, 0.12 to 0.16 wt %.
Si and Mn are added upon melting of steel as a deoxidizer and a deoxidizing/desulfurizing agent, respectively. Such an effect can be obtained by addition of the element in a small amount. Si is a xcex4 ferrite generating element, and therefore, the addition of Si in a large amount may cause undesirable xcex4 ferrite which acts to reduce the fatigue and toughness. The content of Si must be 0.25 wt % or less. In the case of adopting a carbon/vacuum deoxidation process or an electroslag melting process, Si is not required to be added, and rather Si may be not added. In particular, the content of Si may be in a range of 0.10 wt % or less, preferably, in a range of 0.05 wt % or less.
The addition of Mn in a large amount reduces the toughness. The content of Mn must be 0.9 wt % or less. In particular, to improve the toughness, the content of Mn, which is effective as a deoxidizer, may in a range of 0.4 wt % or less, preferably, 0.2 wt % or less.
Cr is effective to increase the corrosion resistance and tensile strength of the alloy; however, the addition of Cr in an amount of 13 wt % or more may cause a xcex4 ferrite structure. The addition of Cr in an amount of less than 8 wt % is insufficient for Cr to exhibit the effect of increasing the corrosion resistance and tensile strength. The content of Cr may be in a range of 8 to 13 wt %. To improve the strength, the content of Cr is preferably in a range of 10.5 to 12.5 wt %, more preferably, 11 to 12 wt %.
Mo is effective to increase the tensile strength of the alloy by its function of promoting solid-solution and precipitation. Such an effect, however, is not large so much, and the addition of Mo in an amount of 3 wt % or more may cause xcex4 ferrite. The content of Mo is limited in a range of 1.5 to 3.0 wt %. In particular, the content of Mo is preferably in a range of 1.8 to 2.7 wt %, more preferably, 2.0 to 2.5 wt %. It is to be noted that W and Co have the same effect as that of Mo.
V and Nb are effective to enhance the tensile strength and improve the toughness by the function of precipitating carbides. When the content of V is 0.05 wt % or less and the content of Nb is 0.02 wt % or less, the above effect is insufficient. The addition of V in an amount of 0.35 wt % or more and Nb in an amount of 0.2 wt % or more may cause xcex4 ferrite. In particular, the content of V may be in a range of 0.15 to 0.30 wt %, preferably, 0.25 to 0.30 wt %; and the content of Nb may be in a range of 0.04 to 0.15 wt %, preferably, 0.06 to 0.12 wt %. It is to be noted that Ta may be added in place of or in combination with Nb.
Ni is effective to enhance the low temperature toughness and prevent occurrence of xcex4 ferrite. When the content of Ni is 2 wt % or less, the effect cannot be sufficiently obtained. When it is more than 3 wt %, the addition effect is saturated. In particular, the content of Ni is preferably in a range of 2.3 to 2.9 wt %, more preferably, 2.4 to 2.8 wt %.
N is effective to improve the tensile strength and prevent occurrence of xcex4 ferrite. When the content of N is less than 0.02 wt %, the effect cannot be sufficiently obtained. When it is more than 0.1 wt %, the toughness is reduced. In particular, the content of N is preferably in a range of 0.04 to 0.08 wt %, more preferably, 0.06 to 0.08 wt %.
The reduction in contents of Si, P and S is effective to increase the low temperature toughness while ensuring the tensile. The contents of Si, P and S are desired to be reduced as much as possible. To improve the low temperature toughness, the content of Si may be in a range of 0.1 wt % or less; the content of P may be in a range of 0.015 wt % or less; and the content of S may be in a range of 0.015 wt % or less. In particular, the content of Si is preferably in a range of 0.05 wt % or less; the content of P is preferably in a range of 0.010 wt % or less; and the content of S is preferably in a range of 0.010 wt % or less. The reduction in contents of Sb, Sn and As is also effective to increase the low temperature toughness, and therefore, the contents of Sb, Sn and As are desired to be reduced as much as possible. However, in consideration of the existing steel-making technical level, the content of Sb may be in a range of 0.0015 wt % or less; the content of Sn may be in a range of 0.01 wt % or less; and the content of As may be in a range of 0.02 wt % or less. In particular, the content of Sb is preferably in a range of 0.001 wt % or less; the content of Sn is preferably in a range of 0.005 wt % or less; and the content of As is preferably in a range of 0.01 wt % or less.
According to the present invention, the ratio (Mn/Ni) is preferably in a range of 0.11 or less.
The heat-treatment of the inventive material is preferably performed by uniformly heating the material at a temperature allowing perfect austenite transformation, that is, in a range of 1000 to 1100xc2x0 C., followed by rapid cooling (preferably, oil-cooling) of the material; heating and keeping to and at a temperature of 550 to 570xc2x0 C., followed by cooling of the material (primary temper); and heating and keeping to and at a temperature of 560 to 680xc2x0 C., followed by cooling of the material (secondary temper), to thereby obtain a full temper martensite structure.
(2) There will be described a reason for limiting the content of each component of the ferrite based heat resisting steel, which is used for a rotor, blade, nozzle, inner casing fastening bolt and an intermediate pressure portion initial diaphragm in a high pressure turbine, an intermediate pressure turbine or a high pressure/intermediate pressure turbine of the inventive steam turbine operable at a temperature of 620 to 640xc2x0 C.
C is an essential element for increasing the high temperature strength by ensuring the quenching ability and precipitating carbides at the tempering step. Also, to obtain the high tensile strength, C is required to be added in an amount of 0.05 wt % or more. However, when the content of C is more than 0.20 wt %, the metal structure becomes unstable upon the alloy is exposed to a high temperature atmosphere for a long time, to reduce the long time creep rupture strength. The content of C is limited in a range of 0.05 to 0.20 wt %, and is preferably in a range of 0.08 to 0.13 wt %, more preferably, 0.09 to 0.12 wt %.
Mn is added as a deoxidizer and the like. The effect can be obtained by the addition of Mn in a small amount. The addition of Mn in a large amount more than 1.5 wt % is undesirable because it reduces the creep rupture strength. In particular, the content of Mn is preferably in a range of 0.03 to 0.20 wt %, or in a range of 0.3 to 0.7 wt %, more preferably, 0.35 to 0.65 wt %. The smaller content of Mn is effective to increase the strength, and the larger content of Mn is effective to improve machinability.
Si is added as a deoxidizer. However, in the case of adopting the steel-making technique such as carbon/vacuum deoxidization process, deoxidization by Si becomes unnecessary. The reduction in content of Si is effective to prevent occurrence of the undesirable xcex4 ferrite structure and to prevent reduction in toughness due to segregation at crystal boundaries and the like. As a result, if Si is added, the content of Si should be limited in a range of 0.15 wt % or less, preferably, 0.07 wt % or less, more preferably, less than 0.04 wt %.
Ni is very effective to increase the toughness and prevent occurrence of xcex4 ferrite. The effect cannot be sufficiently obtained by addition of Ni in an amount of less than 0.05 wt %. Meanwhile, the addition of Ni in an amount more than 1.0 wt % is undesirable because it reduces the creep rupture strength. In particular, the content of Ni is preferably in a range of 0.3 to 0.7 wt %, more preferably, 0.4 to 0.65 wt %.
Cr is an essential element for increasing the high temperature strength and the high temperature oxidation resistance. To achieve the effect, Cr must be added in an amount of 9 wt % at minimum. The addition of Cr in an amount more than 13 wt % may cause the undesirable xcex4 ferrite structure, leading to reduction in the high temperature strength and toughness. The content of Cr is limited in a range of 9 to 12 wt %, preferably, in a range of 10 to 12 wt %, more preferably, 10.8 to 11.8 wt %.
Mo is added to improve the high temperature strength. In the steel containing W in an amount of more than 1 wt % like the inventive steel, however, the addition of Mo in an amount of 0.5 wt % or more reduces the toughness and the fatigue strength. The content of Mo is thus limited in a range of 0.5 wt % or less, preferably, 0.05 to 0.45 wt %, more preferably, 0.1 to 0.2 wt %.
W is an element of suppressing aggregation/coarsening of carbides and promoting solid-solution of a matrix, and therefore, W is effective to significantly increase the long time strength at a high temperature of 620xc2x0 C. or more. The content of W is preferably in a range of 1 to 1.5 wt % for the alloy used at 620xc2x0 C.; in a range of 1.6 to 2.0 wt % for the alloy used at 630xc2x0 C.; in a range of 2.1 to 2.5 wt % for the alloy used at 640xc2x0 C.; in a range of 2.6 to 3.0 wt % for the alloy used at 650xc2x0 C.; and in a range of 3.1 to 3.5 wt % for the alloy used at 660xc2x0 C. The addition of W in an amount of 3.5 wt % or more may cause occurrence of xcex4 ferrite, leading to reduction in toughness. The content of W is thus limited in a range of 1 to 3.5 wt %, preferably, 2.4 to 3.0 wt %, more preferably, 2.5 to 2.7 wt %.
V is effective to increase the creep rupture strength by precipitating a carbo-nitride of V. The effect cannot be sufficiently achieved by addition of V in an amount of less than 0.05 wt %. The addition of V in an amount of more than 0.3 wt % may cause occurrence of xcex4 ferrite, leading to reduction in fatigue strength. The content of V is preferably in a range of 0.10 to 0.25 wt %, more preferably, 0.15 to 0.23 wt %.
Nb is very effective to increase the high temperature strength by precipitating a carbide (NbC); however, the addition of Nb in an excessively large amount causes a coarsened eutectic carbide, particularly, in the case of a large-sized ingot, causing precipitation of xcex4 ferrite which reduces the high temperature strength and fatigue strength. In this regard, the content of Nb is limited in a range of 0.20 wt % or less. Meanwhile, when the content of Nb is less than 0.01 wt %, the effect cannot be sufficiently achieved. In particular, the content of Nb may be in a range of 0.02 to 0.15 wt %, preferably, 0.04 to 0.10 wt %.
Co is an important element which is a factor distinguishing the inventive material from the conventional material. According to the present invention, the addition of Co is effective to significantly improve the high temperature strength as well as the toughness. This is due to interaction with addition of W, and is a phenomenon inherent to the inventive alloy containing W in an amount of 1 wt % or more. To realize the addition effect of Co, the lower limit of Co in the inventive alloy is set at 2.0 wt %. When Co is added in an excessively large amount, not only the effect is saturated but also the toughness is reduced. The upper limit of Co is set at 10 wt %. The content of Co is preferably in a range of 2 to 3 wt % for the alloy used at 620xc2x0 C.; 3.5 to 4.5 wt % for the alloy used at 630xc2x0 C.; 5 to 6 wt % for the alloy used at 640xc2x0 C.; 6.5 to 7.5 wt % for the alloy used at 650xc2x0 C.; and 8 to 9 wt % for the alloy used at 660xc2x0 C.
N is also an important element which is another factor distinguishing the inventive material from the conventional material. N is effective to improve the creep rupture strength and prevent occurrence of the xcex4 ferrite structure. When the content of N is 0.01 wt % or less, the effect cannot be sufficiently achieved, while when it is more than 0.05 wt %, the toughness is reduced and also the creep rupture strength is lowered. In particular, the content of N may be in a range of 0.01 to 0.03 wt %, preferably, 0.015 to 0.025 wt %.
B is effective to increase the high temperature strength by a function of strengthening crystal boundaries and a function of blocking aggregation/coarsening of a M23C6 type carbide because B is dissolved in the M23C6 type carbide in the solid state. To achieve the effect, B is must be added in an amount of 0.001 wt % or more; however, the addition of B in an amount more than 0.03 wt % exerts adverse effect on weldability and forging ability. The content of B is limited in a range of 0.001 to 0.03 wt %, preferably, 0.001 to 0.01 wt %, more preferably, 0.01 to 0.02 wt %.
Ta, Ti and Zr are effective to increase the toughness. To achieve the effect, 0.15 wt % or less of Ta, 0.1 wt % or less of Ti, and 0.1 wt % or less of Zr may be added singly or in combination. In the case of the addition of Ta in an amount of 0.1 wt % or more, the addition of Nb can be omitted.
The rotor shaft, at least the first stage rotating blade, and at least the first stage stationary blade according to the present invention, which are operated at a steam temperature of 620 to 630xc2x0 C., are preferably made from a full temper martensite steel containing 0.09 to 0.20 wt % of C, 0.15 wt % or less of Si, 0.05 to 1.0 wt % of Mn, 9.5 to 12.5 wt % of Cr, 0.1 to 1.0 wt % of Ni, 0.05 to 0.30 wt % of V, 0.01 to 0.06 wt % of N, 0.05 to 0.5 wt % of Mo, 2 to 3.5 wt % of W, 2 to 4.5 wt % of Co, and 0.001 to 0.030 wt % of B, the balance being 77 wt % or more of Fe. The rotor shaft and the like, which are operated at a temperature of 635 to 660xc2x0 C., are preferably made from a full temper martensite steel having the same composition as described above except that the content of Co is set in a range of 5 to 8 wt % and the balance is set at 78 wt % or more of Fe. Further, the rotor shaft and the like, which are operated at a temperature of 620 to 660xc2x0 C., are preferably made from a steel having the same composition as described above except that the content of Mn is reduced to a value in a range of 0.03 to 0.2 wt % and the content of B is reduced to a value in a range of 0.001 to 0.01 wt % for increasing the strength. In particular, a steel suitable to be used at a temperature of 630xc2x0 C. or less and a steel suitable to be used at a temperature of 630 to 660xc2x0 C. are preferably obtained by addition of 2 to 4 wt % of Co and 0.001 to 0.01 wt % of B, and addition of 5.5 to 9.0 wt % of Co, and 0.01 to 0.03 wt % of B to a basic composition containing 0.09 to 0.20 wt % of C, 0.1 to 0.7 wt % of Mn, 0.1 to 1.0 wt % of Ni, 0.10 to 0.30 wt % of V, 0.02 to 0.05 wt % of N, 0.05 to 0.5 wt % of Mo, 2 to 3.5 wt % of W, respectively.
For the rotor shaft or the like, the Cr equivalent calculated by the equation to be described later is preferably in a range of 4 to 10.5, more preferably, 6.5 to 9.5.
The rotor material used for each of the high pressure turbine and the intermediate pressure turbine of the steam turbine of the present invention preferably has a uniform temper martensite structure because the presence of a xcex4 ferrite structure reduces the fatigue strength and the toughness. To obtain the temper martensite structure, it is required to set the Cr equivalent calculated by the above equation in a range of 10 or less by adjusting the composition. When the Cr equivalent is excessively low, the creep rupture strength is reduced. The Cr equivalent is limited in a range of 4 or more. In particular, the Cr equivalent is preferably in a range of 5 to 8.
The steam turbine rotor, operable in steam at a temperature of 620xc2x0 C. or more, of the present invention is produced in the following procedure. A raw material having a specific composition is melted in an electric furnace, followed by carbon/vacuum deoxidation, and cast in a metal mold to form an ingot. The ingot is then forged to prepare an electrode bar. The electrode bar is melted by an electroslag re-melting process to form an ingot, and the ingot is forged into a rotor shape. The forging must be performed at a temperature of 1150xc2x0 C. or less for preventing occurrence of forging crack. The forged steel is annealed, and is subjected to quenching (quenching temperature: 1000 to 1100xc2x0 C.) and to double temper (temper temperature: 550 to 650xc2x0 C., 670 to 770xc2x0 C.).
Each of the blade, nozzle, inner casing fastening bolt, intermediate pressure portion first stage diaphragm according to the present invention is vacuum-melted and is cast in a die in vacuum to prepare an ingot. The ingot is hot-forged at the same temperature as described above into a specific shape. The forged steel is heated at a temperature of 1050 to 1150xc2x0 C. and water-quenched or oil-quenched, followed by temper at a temperature of 700 to 800xc2x0 C., and is machined into a blade having a specific shape. The vacuum melting is performed under a vacuum of 10xe2x88x921 to 10xe2x88x924 mm Hg. The heat resisting steel of the present invention can be used for all stages of blades and nozzles of each of the high pressure portion and the intermediate pressure portion, and particularly, the steel is required to be used for the first stage blade and nozzle.
(3) There will be described the composition of a material used for a rotor shaft of each of the high pressure turbine, intermediate pressure turbine or high pressure/intermediate pressure integral type turbine of the steam turbine of the present invention, which is operable at a temperature of 600 to less than 620xc2x0 C.
C is required to be added in an amount of 0.05 wt % or more for increasing the tensile strength; however, when the content of C is more than 0.25 wt %, the structure becomes unstable when the alloy is exposed to a high temperature atmosphere for a long time, leading to reduction in long time creep rupture strength. The content of C is limited in a range of 0.05 to 0.25 wt %, preferably, 0.1 to 0.2 wt %.
Nb is very effective to increase the high temperature strength. However, the addition of Nb in an excessively large amount precipitates a corsened carbide of Nb, particularly, for a large-sized ingot; reduces the concentration of C in the matrix, resulting in the reduced strength; and precipitate xcex4 ferrite which reduces the fatigue strength. The content of Nb must be limited in a range of 0.15 wt % or less. Meanwhile, when the content of Nb is less than 0.02 wt %, the effect cannot be sufficiently achieved. The content of Nb is preferably in a range of 0.07 to 0.12 wt %.
N is effective to improve the creep rupture strength and prevent generation of xcex4 ferrite. When the content of N is less than 0.025 wt %, the effect cannot be sufficiently achieved. When it is more than 0.1 wt %, the toughness is significantly reduced. The content of N is preferably in a range of 0.04 to 0.07 wt %.
Cr is effective to increase the high temperature strength. However, the addition of Cr in an amount more than 13 wt % causes occurrence of xcex4 ferrite, and the addition of Cr in an amount of less than 8 wt % makes poor the corrosion resistance against high temperature/high pressure steam. The content of Cr is preferably in a range of 10 to 11.5 wt %.
V is effective to increase the creep rupture strength. When the content of V is less than 0.02 wt %, the effect cannot be sufficiently achieved, while when it is more than 0.5 wt %, there occurs xcex4 ferrite which reduces the fatigue strength. The content of V is preferably in a range of 0.1 to 0.3 wt %.
Mo is effective to improve the creep strength by a function of reinforcement of solid-solution and precipitation hardening. When the content of Mo is less than 0.5 wt %, the effect cannot be sufficiently achieved, while when it is more than 2 wt %, there occurs xcex4 ferrite which reduces the toughness and creep rupture strength. In particular, the content of Mo is preferably in a range of 0.75 to 1.5 wt %.
Ni is very effective to increase the toughness and prevent occurrence of xcex4 ferrite. However, the addition of Ni in an amount more than 1.5 wt % undesirably reduces the creep rupture strength. The content of Ni is preferably in a range of 0.4 to 1 wt %.
Mn is added as a deoxidizer. The effect can be achieved by the addition of a small amount of Mn. The addition of Mn in a large amount more than 1.5 wt % reduces the creep rupture strength. The content of Mn is preferably in a range of 0.5 to 1 wt %.
Si is also added as a deoxidizer. However, in the case of adopting a steel-making technique such as vacuum/carbon deoxidation, the deoxidization by Si becomes unnecessary. The reduction in the content of Si is effective to prevent precipitation of xcex4 ferrite and improve the toughness. For this reason, the content of Si must be limited in a range of 0.6 wt % or less. If it is added, the content of Si is preferably set at 0.25 wt %.
W is an element capable of significantly increasing the high temperature strength in a slight amount. When the content of W in an amount less then 0.1 wt %, the effect is small, while when it is more than 0.65 wt %, the strength is rapidly reduced. The content of W should be in a range of 0.1 to 0.65 wt % or less. On the other hand, when the content of W in an amount more than 0.5 wt %, the toughness is significantly reduced. For a member requiring the toughness, the content of W may be set at a value less than 0.5 wt %. The content of W is preferably in a range of 0.2 to 0.45 wt %.
Al is an effective element as a deoxidizer. The content of Al may be set at 0.02 wt % or less. The addition of Al in an amount more than 0.02 wt % reduces the high temperature strength.
(4) As for the rotor shaft of the steam turbine, made from the 12% Cr based martensite steel according to the present invention, buildup layers having a high bearing characteristic are preferably formed by welding on the surface of a base material for forming a jounal portion of the rotor shaft. To be more specific, three to ten buildup layers may be formed by welding using a welding material made from a steel. In this case, the first, second, third, and fourth layers are built up by welding using welding materials of which the Cr contents are sequentially lowered, and the fifth layer and the later layers are built up by welding using welding materials of which the Cr contents are identical to each other. Further, the Cr content of the welding material used for welding of the first layer is smaller 2 to 6 wt % than that of the base material, and the Cr content of each of the fourth layer and the later layers is set at 0.5 to 3 wt % (preferably, 1 to 2.5 wt %).
In the present invention, to improve the bearing characteristic of the jounal portion, buildup welding is preferable in terms of high safety. The buildup welding, however, may replaced with shrinkage fit or insertion of a sleeve made from a low alloy steel containing Cr in an amount of 1 to 3 wt %.
To gradually change the content of Cr in buildup layers, it is desired to provide three layers or more; however, if ten layers or more are provided, the effect is saturated. The total thickness of the buildup layers is represented by about 18 mm after final finishing. To ensure such a total thickness, it is desired to provide at least five buildup layers excluding a cutting allowance for final finishing. Each of the third layer and the later layers preferably has a martensite structure in which a carbide is precipitated. In particular, the welding layer of each of the fourth layer and the later layers preferably contains 0.01 to 0.1 wt % of C, 0.3 to 1 wt % of Si, 0.3 to 1.5 wt % of Mn, 0.5 to 3 wt % of Cr, and 0.1 to 1.5 wt % of Mo, the balance being Fe.
(5) There will be described a reason for limiting the content of each component of the ferrite based heat resisting steel used for an inner casing governor valve box, combination re-heat valve box, main steam lead pipe, main steam inlet pipe, re-heat inlet pipe, high pressure turbine nozzle box, intermediate pressure turbine first stage diaphragm, high pressure turbine main steam inlet flange, elbow, and main steam stop valve of each of the high pressure turbine, intermediate pressure turbine, and high pressure/intermediate pressure turbine.
By adjusting the Ni/W ratio in a range of 0.25 to 0.75, the ferrite based heat resisting cast steel as the casing material satisfies characteristics required for the high pressure and intermediate pressure inner casings, main steam stop valve and governor valve casing of an ultrasuper critical pressure turbine operated at 621xc2x0 C. and 250 kgf/cm2 or more, that is, exhibits a 105 h creep rupture strength (at 625xc2x0 C.) of 9 kgf/mm2 or more and an impact absorption energy (at room temperature) of 1 kgf-m or more.
In the ferrite based heat resisting cast steel as the casing material according to the present invention, to obtain a high temperature strength, a low temperature toughness, and a high fatigue strength, it is desired to adjust the composition such that the Cr equivalent calculated by the above equation is in a range of 4 to 10.
The 12% Cr based heat resisting steel of the present invention, which is operated in steam at a temperature of 621xc2x0 C. or more, must exhibit a 105 h creep rupture strength (at 625xc2x0 C.) of 9 kgf/mm2 or more and an impact absorption energy (at room temperature) of 1 kgf-m or more, and to ensure a higher reliability, it preferably exhibits a 105 h creep rupture strength (at 625xc2x0 C.) of 10 kgf/mm2 or more and an impact absorption energy (at room temperature) of 2 kgf-m or more.
C is required to be added in an amount of 0.06 wt % or more for increasing the tensile strength. When the content of C is more than 0.16 wt %, the metal structure becomes unstable when the alloy is exposed to a high temperature atmosphere for a long time, leading to reduction in long time creep rupture strength. The content of C is limited in a range of 0.06 to 0.16 wt %, preferably, 0.09 to 0.14 wt %.
N is effective to improve the creep rupture strength and prevent occurrence of a xcex4 ferrite. When the content of N is less than 0.01 wt %, the effect cannot be sufficiently achieved, while when it is more than 0.1 wt %, the effect is already saturated, and the toughness is reduced and the creep rupture strength is lowered. The content of N is preferably in a range of 0.02 to 0.06 wt %.
Mn is added as a deoxidizer. The effect can be achieved by the addition of a small amount of Mn. The addition of Mn in an amount more than 1 wt % reduces the creep rupture strength. The content of Mn is preferably in a range of 0.4 to 0.7 wt %.
Si is also added as a deoxidizer. However, in the case of adopting a steel-making technique such as vacuum/carbon deoxidation, the deoxidization by Si becomes unnecessary. The reduction in content of Si is effective to prevent occurrence of a undesirable xcex4 ferrite structure. If Si is added, the content of Si must be limited in a. range of 0.5 wt % or less, preferably, 0.1 to 0.4 wt %.
V is effective to increase the creep rupture strength. When the content of V is less then 0.05 wt %, the effect cannot be sufficiently achieved, while when it is more than 0.35 wt %, there occurs xcex4 ferrite which reduces fatigue strength. The content of V is preferably in a range of 0.15 to 0.25 wt %.
Nb is very effective to increase the high temperature strength. However, the addition of Nb in an excessively large amount causes a coarsened eutectic carbide of Nb, particularly, in the case of a large-sized ingot, to rather reduce the strength and precipitate xcex4 ferrite which reduces the fatigue strength. The content of Nb is limited in a range of 0.15 wt % or less. When the content of Nb is less than 0.01 wt %, the effect cannot be sufficiently achieved. In the case of a large-sized ingot, particularly, the content of Nb may be in a range of 0.02 to 0.1 wt %, preferably, 0.04 to 0.08 wt %.
Ni is very effective to increase the toughness and prevent occurrence of xcex4 ferrite. When the content of Ni is less than 0.2 wt %, the effect cannot be sufficiently achieved, while when it is more than 1.0 wt %, the creep rupture strength is undesirably reduced. The content of Ni is preferably in a range of 0.4 to 0.8 wt %.
Cr is effective to improve the high temperature strength and high temperature oxidation. When the content of Cr is more than 12 wt %, there occurs a undesirable xcex4 ferrite structure, while when it is less than 8 wt %, the oxidation resistance against high temperature/high pressure steam becomes insufficient. The addition of Cr is effective to increase the creep rupture strength; however, excessively large amount of Cr causes a undesirable xcex4 ferrite structure and reduces the toughness. The content of Cr is preferably in a range of 8.0 to 10 wt %, more preferably, in a range of 8.5 to 9.5 wt %.
W is effective to significantly increase the high temperature/long time strength. When the content of W is less than 1 wt %, the effect becomes insufficient if the heat resisting steel is used at a temperature of 620 to 660xc2x0 C., while when it is more than 4 wt %, the toughness is reduced. The content of W is preferably in a range of 1.0 to 1.5 wt % for the alloy used at 620xc2x0 C.; in a range of 1.6 to 2.0 wt % for the alloy used at 630xc2x0 C.; in a range of 2.1 to 2.5 wt % for the alloy used at 640xc2x0 C.; in a range of 2.6 to 3.0 wt % for the alloy used at 650xc2x0 C.; and in a range of 3.1 to 3.5 wt % for the alloy used at 660xc2x0 C.
W has interaction with Ni, and both the strength and toughness can be increased by setting the ratio Ni/W in a range of 0.25 to 0.75.
Mo is effective to increase the high temperature strength. However, for the alloy containing W in an amount more than 1 wt % like the cast steel of the present invention, the addition of Mo in an amount of 1.5 wt % or more reduces the toughness and fatigue strength. The content of Mo to be added is limited in the range of 1.5 wt % or less, preferably, 0.4 to 0.8 wt %, more preferably, 0.55 to 0.70 wt %.
Ta, Ti and Zr are effective to increase the toughness. To achieve the effect, 0.15 wt % or less of Ta, 0.1 wt % or less of Ti, and 0.1 wt % or less of Zr may be added singly or in combination. In the case of the addition of Ta in an amount of 0.1 wt % or more, the addition of Nb can be omitted.
The heat resisting cast steel as the casing material of the present invention preferably has a uniform temper martensite structure because the presence of a xcex4 ferrite structure reduces the fatigue strength and the toughness. To obtain the temper martensite structure, it is required to set the Cr equivalent calculated by the above equation in a range of 10 or less by adjusting the composition. When the Cr equivalent is excessively low, the creep rupture strength is reduced. The Cr equivalent is limited in a range of 4 or more. In particular, the Cr equivalent is preferably in a range of 6 to 9.
B is effective to significantly increase the creep rupture strength at high temperatures (620xc2x0 C. or more). The addition of B in an amount more than 0.003 wt % degrades weldability, and therefore, the upper limit of the content of B is set at 0.003 wt %. In the case of the alloy used for a large-sized casing, the upper limit of the content of B may be set at 0.0028 wt %. The content of B is preferably in a range of 0.0005 to 0.0025 wt %, more preferably, 0.001 to 0.002 wt %.
The casing, which covers high pressure steams at a temperature of 620xc2x0 C. or more, is applied with a high stress due to an inner pressure. Accordingly, to prevent occurrence of creep rupture, the casing is required to exhibit a 105 h creep rupture strength of 10 kgf/mm2 or more. Further, since the casing is applied with a thermal stress when the metal temperature is low upon starting, it must exhibit an impact absorption energy (at room temperature) of 1 kgf-m or ore for preventing occurrence of brittle fracture. For the casing material used on the higher temperature side, its strength can be increased by addition of Co in an amount of 10 wt % or less. To be specific, the content of Co is preferably in a range of 1 to 2 wt % for the alloy used at 620xc2x0 C.; in a range of 2.5 to 3.5 wt % for the alloy used at 630xc2x0 C.; in a range of 4 to 5 wt % for the alloy used at 640xc2x0 C.; in a range of 5.5 to 6.5 wt % for the alloy used at 650xc2x0 C.; and in a range of 7 to 8 wt % for the alloy used at 660xc2x0 C. For the alloy used at a temperature of 600 to 620xc2x0 C., Co may be not added.
To produce a casing material with less defects, a large-size ingot having a weight of about 50 ton must be prepared, which requires a high level steel-making technique. The heat resisting cast steel as the casing material of the present invention is produced by melting a raw material having a specific composition in an electric furnace, followed by ladle refining, and casting molten steel in a sand mold. In this case, a high quality ingot with less casting defects such as shrinkage cavities can be obtained by sufficiently refining and deoxidizing molten steel before casting.
The above cast steel is annealed at a temperature of 1000 to 1150xc2x0 C., and heated at a temperature of 1000 to 1100xc2x0 C. and rapidly cooled (normalizing), followed by double temper (550 to 750xc2x0 C., 670 to 770xc2x0 C.), to obtain a steam turbine casing operable in steam at a temperature of 621xc2x0 C. or more. When each of the annealing temperature and normalizing temperature is less than 1000xc2x0 C., a carbo-nitride cannot be sufficiently dissolved in the solid-state, while when it is excessively high, there may occur coarsening of crystal grains. The double temper perfectly decomposes retained austenite to form a uniform temper martensite. In accordance with the above process, there can be produced a steam turbine casing having a 105 h creep rupture strength (at 625xc2x0 C.) of 10 kgf/mm2 or more and an impact absorption energy (at room temperature) of 1 kgf-m or more. Such a casing is operable in steam at a temperature of 620xc2x0 C. or more.
When the content of O is more than 0.015 wt %, the high temperature strength and the toughness are reduced, and therefore, the content of O is limited in a range of 0.015 wt % or less, preferably, 0.010 wt % or less.
For the casing material of the present invention, the Cr equivalent is set at the same value as described above to reduce the xcex4 ferrite amount to a value of 5 wt % or less. The xcex4 ferrite amount is preferably reduced to zero.
While the inner casing is made from a cast steel, the other parts are preferably made from forged steels.
(6) Others
(A) The rotor shaft for the low pressure steam turbine is preferably made from a low alloy steel which contains 0.2 to 0.3 wt % of C, 0.1 wt % or less of Si, 0.2 wt % or less of Mn, 3.2 to 4.0 wt % of Ni, 1.25 to 2.25 wt % of Cr, 0.1 to 0.6 wt % of Mo, and 0.05 to 0.25 wt % of V, and which has a full temper bainite structure. This rotor shaft is preferably produced in the same manner as that for the above rotor shaft of the high pressure or intermediate pressure steam turbine. In particular, the rotor shaft is preferably produced by a super clean process using a raw material in which the amount of Si is reduced to a value of 0.05 wt % or less, the amount of Mn is reduced to a value of 0.1 wt % or less, and the total amount of other impurities such as P, S, As, Sb and Sn is reduced as much as possible, for example, to a value 0.025 wt % or less. In this case, the amount of each of P and S is preferably in a range of 0.010 wt % or less; the amount of each of Sn and As is preferably in a range of 0.005 wt % or less; and the amount of Sb is preferably in a range of 0.001 wt % or less.
(B) The final stage blade and nozzle for the low pressure turbine is preferably made form a full temper martensite steel containing 0.05 to 0.2 wt % of C, 0.1 to 0.5 wt % of Si, 0.2 to 1.0 wt % of Mn, 10 to 13 wt % of Cr, and 0.04 to 0.2 wt % of Cr.
(C) The inner casing and outer casing for the low pressure turbine are preferably made from a carbon cast steel containing 0.2 to 0.3 wt % of C, 0.3 to 0.7 wt % of Si, and 1 wt % of Mn.
(D) The main steam stop valve casing and steam governor valve casing are preferably made from a full temper martensite steel containing 0.1 to 0.2 wt % of C, 0.1 to 0.4 wt % of Si, 0.2 to 1.0 wt % of Mn, 8.5 to 10.5 wt % of Cr, 0.3 to 1.0 wt % of Mo, 1.0 to 3.0 wt % of W, 0.1 to 0.3 wt % of V, 0.03 to 0.1 wt % of Nb, 0.03 to 0.08 wt % of N, and 0.0005 to 0.003 wt % of B.
(E) As the final stage rotating blade for the low pressure turbine, there may be used a Ti alloy in place of the 12% Cr based steel. In particular, the final stage rotating blade having a length of 40 inches or more is made from a Ti alloy containing 5 to 8 wt % of Al and 3 to 6 wt % of V; the blade having a length of 43 inches is made from a high strength Ti alloy containing 5.5 to 6.5 wt % of Al and 3.5 to 4.5 wt % of V; and the blade having a length of 46 inches is made from a higher Ti alloy containing 4 to 7 wt % of Al, 4 to 7 wt % of V and 1 to 3 wt % of Sn.
(F) The outer casing for each of the high pressure turbine, intermediate pressure turbine and high pressure/intermediate pressure turbine is made from a cast steel which contains 0.10 to 0.20 wt % of C, 0.05 to 0.6 wt % of Si, 0.1 to 1.0 wt % of Mn, 0.1 to 0.5 wt % of Ni, 1 to 2.5 wt % of Cr, 0.5 to 1.5 wt % of Mo, and 0.1 to 0.35 wt % of V, and preferably, at least one of 0.025 wt % or less of Al, 0.0005 to 0.004 wt % of B, and 0.05 to 0.2 wt % of Ti, and which has a full temper bainite structure. In particular, there is preferably used a cast steel containing 0.10 to 0.18 wt % of C, 0.20 to 0.60 wt % of Si, 0.20 to 0.50 wt % of Mn, 0.1 to 0.5 wt % of Ni, 1.0 to 1.5 wt % of Cr, 0.9 to 1.2 wt % of Mo, 0.2 to 0.3 wt % of V, 0.001 to 0.005 wt % of Al, 0.045 to 0.10 wt % of Ti, and 0.0005 to 0.0020 wt % of B. In this composition, more preferably, the Ti/Al ratio is in a range of 0.5 to 10.
(G) The first stage blade for each of the high pressure turbine, intermediate pressure turbine, and high pressure/intermediate pressure turbine (high pressure side and the intermediate pressure side) at a steam temperature of 625 to 650xc2x0 C. is made from a Ni based alloy containing 0.03 to 0.20 wt % (preferably, 0.03 to 0.15 wt %), 12 to 20 wt % of Cr, 9 to 20 wt % of Mo (preferably, 12 to 20 wt %), 12 wt % or less of Co (preferably, 5 to 12 wt %), 0.5 to 1.5 wt % of Al, 1 to 3 wt % of Ti, 5 wt % or less of Fe, 0.3 wt % or less of Si, 0.2 wt % or less of Mn, 0.003 to 0.015 wt % of B, and one kind or more of 0.1 wt % or less of Mg, 0.5 wt % or less of a rare earth element and 0.5 wt % or less of Zr. In addition, the wording xe2x80x9cor lessxe2x80x9d contains 0 wt %. The above alloy is forged, followed by solution treatment, and subjected to ageing treatment at a temperature of 700 to 870xc2x0 C.